The Inland Sea, Wilton's Music Hall, London

Strange noises echo throughout The Inland Sea (and echo they do indeed in this bare and narrow theatre, though it might help if the actors didn't boom so much). The ancient oaks groan and sigh as they are felled according to the designs of Capability Brown. Brown's luckless younger brother screams as he is digitally sodomised by a villager who wants to show him true pleasure. The earth buckles and creaks as the spirit of a murdered girl heaves her way out of it. But the loudest motif in Naomi Wallace's play is the sound of an author straining for a message that eludes her grasp.

On a Yorkshire estate in the 1760s, Asquith Brown (a fictional character) has been charged with executing his busy brother's grand scheme of improving nature. But each time Capability visits for a progress check, there is more to worry about. The new landscaping calls for not only sweeping away a precious little garden, which looks like a game board dotted with conifers made of green cheese: it means the creation of a lake, the sculpting of new hills, and the removal of unsightly and irrelevant features, such as peasants. Swept out with digging tools, the villagers return with pitchforks, though one forms a temporary alliance with Asquith, who is socially and sexually insecure. Meanwhile, the work, carried on by soldiers and by labourers from London, disinters crimes and secrets.

In summary The Inland Sea may sound like a clever romantic tragedy with some apt social comment. And so it might have been had it been written by someone else. The play might even have been a successful poetic drama, slipping in and out of reality. But Wallace not only combines these two unlikely partners; she spurns both reality and poetry for preciosity (Come to the replica peasant society! See folk tunes created before your eyes!) and sex obsession.

When Hesp, a randy widow, isn't thrusting her fingers up Asquith's backside, she's ordering him to expose himself to her or bragging to her mother about the quantity of her vaginal secretions. Capability, telling his brother that his problems stem from faulty masturbation, explains the proper technique with the aid of a folding ruler. Peasant wisdom is accounted for by Hesp's mother ("I've said it before: let's wait and see"). Peasant, or working-class, poesy is represented by a laconic black sailor ("The ocean. The winds. The butchering. The tea... The sighs. The exchange. The salt. The flesh") and a garrulous vagrant ("Hurrump, hurrah, hooray. Shhh. Only it wasn't in the month of May").

In this Oxford Stage Company production, directed by Dominic Dromgoole, Michael Gould makes a sympathetic Asquith, Jo McInnes a zestful Hesp. But whether dealing with horticulture or uphill gardening this murky, stagnant play is damned hard work.

To 28 April, 020-7836 9712